In machining performed by a machine tool, a pallet carrying device is generally used with the machine tool to place a pallet having a workpiece mounted thereon on the table of the machine tool or to remove a pallet having a machined workpiece mounted thereon from the table, thereby saving labor and improving efficiency of the operation. Such a pallet carrying device is required to be arranged adjacent to a machining area of the machine tool. On the other hand, an operation area for performing various operations including monitoring machining of a workpiece by the machine tool and removing chips is required to be adjacent to the machining area of the machine tool.
However, of all the sides surrounding the machining area, the two sides, i.e., the left and right sides are sometimes occupied by obstacles in addition to a column side. For example, a vertical machine tool having a rotational axis of a spindle extending vertically (i.e., in a Z-axis direction) sometimes uses what is called a trunnion table capable of turning a pallet about a turning axis extending horizontally in lateral direction (i.e., in an X-axis direction) in order to make sophisticated machining possible. In such a case, in order to support a pallet mount on a table so as to be able to turn about a turning axis, a pair of support posts provided so as to be opposed to each other in the X-axis direction, and therefore the left and right sides of the machining area of the machine tool are occupied by the support posts, i.e., obstacles. Therefore, both the machining area and a pallet changer have to be arranged on the front side (front surface) free of obstacles, with the result that the pallet carrying device is arranged between the operation area and the machining area. As a result, the pallet carrying device inconveniently becomes an obstacle to the operation, such as monitoring and chip removal.
In order to solve the above problem, Japanese Unexamined Patent Publication Nos. 9-155677 and 2003-80433 propose a pallet carrying device in which a pallet loader for carrying a pallet is adapted to be movable and an operation area can be secured by retreating the pallet loader from a pallet change position in front of the machining area (on the opposite side of a table from a column) after completely changing the pallet.
However, both of the pallet carrying devices disclosed in Japanese Unexamined Patent Publication Nos. 9-155677 and 2003-80433 pose a problem that the pallet on the table is pulled out into the operation area in front of the machining area, and therefore an operator cannot enter the operation area during the pallet changing operation. Further, both of the pallet carrying devices disclosed in Japanese Unexamined Patent Publication Nos. 9-155677 and 2003-80433 pose a problem that the pallet loader moves in the operation area, and therefore safety of the operator is reduced.